Process and apparatus for impregnating fibrous sheet material



M y 17, 1938 v c. E. Lmsco'rr 2,117,432

PROCESS AND APPARATUS FOR IMPREGNATING FIBROUS SHEETMATERIAL Filed Feb.7, 1935 'INVENTOR 7 6747/71? M7460 ATTORNEY Patcnted'May 17, loss Um'rsoSTATES ffj 2,117,432

PATENT orr cl:

PROCESS AND AIPABATUS FOR MEG- .NATING I'IBROUS SHEET MATERIAL chemia.

Linscott, Bidgcwood, 11.3., assisnor to United States Rubber Company, N.Y., a corporation of New Jersey New Yorlr,

Application rm 1, 1935, Serial No. am 3.0lahns. (cl. si-ss) woven orknitted fabrications of thread and yarn are commonly impregnated withrubber compositions, such as rubber latex, by passing the materialthroush a tanlr of the latex and thence ,between squeeze rolls. In sucha process, especially where light weight and wide fabrics areinterstices of the material is displaced by the impregnatingcomposition, creating large amounts of ,undesirable foam in theimpregnating fluid.

Furthermore, when it has been desired to coat 1' both sides of a fabricby conventional spreader methods, it has been necessary-to coat firstone side and dry the material, then to coat theother side and dry again,a minimum of two spreader operations thus being required.

The present invention relates to the impregnation of fibrous sheetmaterial with fluid rubber compositions without the use of squeezerolls, thereby eliminating the disadvantages incident to that method ofimpregnation. It also provides a process and apparatus whereby flbroussheet material may be impregnated, and coated on both faces in oneoperation by'direct application of a fluid rubber composition to oneface only of the sheet material. It also makes it possible to use, withonly minor changes, the same type of machines for latex impregnation asfor conventional latex spreading.

In the coating of fabrics on one side only with latex according tocommon practice, trouble is frequently experienced due to the tendencyof the latex to strike through the fabric at various points rubber overthe entire upper and lower faces in a single spreading operation.

According to the present invention, the fluid rubber composition isapplied directly, to the upper surface only of the travelling flbroussheet material. and is caused to penetrate into and through sheetmaterial to provide a coating on both sides thereof. A convenient methodof accomplishing this is by, means of one or more spreading devices androllers frictionally engag-- ing the upper face of the sheet material,the rollers preferably rotating in the direction opposite to thedirection of travel of the material. It is also possible to use astationary roll or a roller driven in the same direction as the travelof the material and driven either by the moving fabric itself or byexternal means. The roller itself may be a part of the means forapplying the composition as well as the means for driving it into thetravelling material. The penetration of the composition into and throughthe sheet material is also aided by the hydrostatic pressure of a bankof the fluid rubber composition maintained upon the material between therollers and spreading devices. The composition is then distributed asdesired and excess composition removed to the extent desired by asuitable arrangement of wiper and scraper knives frictionally engagingthe upper and lower faces-of the sheet material.

It is desirable that the rubber composition or the fibrous sheetmaterial, or both, have such characteristics that the sheet material isreadily wetted by theiiuid composition, in order to facilitate thepenetration of the composition into and through the sheet material. Forthis purpose either the rubber composition, or the sheet material, orboth, may be treated with a suitable hols.

The drawing illustrates more or less diagrammatically one typeof-apparatus for impregnating fibrous sheet material.

Referring more particularly to the figure, which is merely exemplary ofthe invention and illustrates a present preferred embodiment thereof,the fibrous sheet material I, in the form of a woven fabric, forexample, is unwound from the roll 2 and drawn under tension through theimpregnating means and drier to be described below and onto a winduproll 3. The fabric as it advances from the roll 2 passes under asmooth-faced roller 4 rotating as shown by the arrows in a directionopposite to the direction of travel of the fabric and thence under aspreading device such as doctor I. The surface of the roller 4frictionally engages the upper surface of the fabric and drives into thesame the latex 5 which is provided between the roller and the spreadingdevice in the form of a pool or bank fed from the latex supply 6 andconfined by the upper surface of the fabric i, the roller 4, the doctorI, and by stops or guides 8 situated on each side of the fabric betweenthe roller 4 and spreader l. Latex from the pool or bank 5 is driveninto and through the advancing fabric by virtue of the rotation of theroller 4 and the pressure of the tensioned fabric against the roller,these actions being supplemented by the hydrostatic pressure of the bank5. The result of this process is that both the threads or yarnsconstituting the fabric become coated or impregnated, and a substantialpart of the latex strikes through the interstices over the entire areaof the fabric and exudes upon the under side of the fabric in the formof small globules or buttons or extending fingers adhering to thefabric. In order to minimize or nullify any tendency of surface tensionor capillarity to draw the exuded latex back into the body of thefabric, it is preferred that the fluid latex composition have arelatively high viscosity and yield value, preferably at least severaltimes the values for uncompounded normal latex. Concentrated latices aretherefore suitable, and may if desired be further thickened by variousknown means. The spreader I regulates the thickness of the layer offluid rubber composition retained on the upper surface of the fabric,which composition may be subsequently smoothed out or partially scrapedoff, as desired, by means of one or more scraper knives 9 arranged atsuitable angles along the path of travel of the fabric. Thus, bypermitting a relatively small amount of latex to be retained on theupper side of the fabric as it emerges from under the spreading deviceI, or by removing the excess of latex by means of scrapers 9, the amountof latex remaining on the upper side of the fabric may be so regulatedthat the individual threads of the fabric, coated with rubber,

stand out in relief, with the latex webbing across the interstices toform saucer-shaped depressions which are closed at the bottom, betweenthe threads. In other words, the film deposited on the upper face of thefabric may be continuous, but irregular in contour, following the weaveof the fabric. Or a greater amount of the latex may be retained on theupper face of the fabric so as to provide a smooth, even coating. Thefluid rubber composition which exudes upon the under side of the fabricmay be smoothed.out and distributed evenly over the under side of thefabric by wiper knives l arranged at a suitable sloping angle to thefabric. After the desired smoothing operations, the fabric may be passedthrough a drying tunnel conventionally shown at H and then wound up asat 3, the coated fabric being drawn through the drying tunnel undersufficient tension to hold the fabric out of contact with the presentinvention with a vulcanizable latex composition as follows:

Rubber (as twice creamed latex 66%) 100 Formaldehyde 2, Sodium isopropylnaphthalene sulfonate- 1. 25, Water 5. 0

Oleic acid g 2. 0 2,2-di-p-phenylol-propane 2 0 Water 18.0 Ammoniumhydroxide -(28%) 5.0

Stearic acid .25

Bleached Montan wax 1 Casper w 75 Water 6. 0 Ammonium hydroxide (28%) 5Whiting 5.0 Sulfur 1. 25 Zinc dimethyl dithiocarbamate .65 Zinc oxide .1Sodium isopropyl naphthalene sulfonate .1 Oleic acid 1 Ammoniumhydroxide 1 Water, 4. 5

This composition was compounded by mixing the various materials, theingredients being added to the latex in groups as indicated above, theliquids as emulsions and the solids as a paste, and the whole dilutedwith water to a water content of 50%. The various ingredients of such alatex composition may be, varied as well known in the art or other latexcompositions substituted, the above composition being merely cited asone example of a latex composition that has been found satisfactory forthe purpose. A so-called 4.75 cotton sheeting (4.75 running yards perpound of 39 inch width), having a thread count of 68 x 72 (threads perinch of warp and weft, respectively) was fed under considerable tensionat about 24 feet per minute under a smooth steel roller two inches indiameter rotating about 70 revolutions per minute in a directionopposite to the direction of travel of the fabric. A reservoir or bankof the latex equal to or greater than the height of the roller wasprovided on the upper surface of the fabric on the egress side of theroller and confined by the roller and by aspreading device or doctorsituated two inches from the roller along the path of travel of thefabric. the fabric passed under the roller and spreading device, theunder side of the fabric became covered with exuded globules of latexwhich had struck through the interstices of the fabric. The coatings onthe upper and lower surfaces were smoothed out by scraper knives and thethus impregnated and coated fabric was dried in a drying tunnel at200-220 F. Further coats of latex, as desired, were applied to either orboth sides in the usual manner and the finished fabric vulcanized at 225F. for 45 minutes.

Various modifications of the illustration in the drawing may be resortedto. For example, the fluid rubber composition may first be applied tothe surface of the travelling sheet material by means of a spreadingdevice and after such application the sheet material may be passed undera rotating roller such as roller 4 to drive the composition into thematerial. If desired,

anus:

the roller, the rubber composition being confined only by the roller andthe surface of the inclined sheet material and the stops at the sides ofthefabric, and being carried from the reservoir or bank on theuppersurface of the fabric and flowing down the inclined fabric by gravity,as shown in the McGavack Patent 1,946,090, to form a smooth coherentcoating. The spreading device, if used in conjunction with the roller 4,as shown at I, or if used to apply the fluid rubber composition to thesheet material prior to passage under the roller 4, may take the form ofa conventional doctor, as shown, or may take the form of a groovedspreading device, as shown in the patent to Charles Dennison No.1,975,195. It is possible to obtain even better impregnation by having abank of latex in front of as well as behind the rotating roll 4. It isalso possible to place the blade 1 ahead of bank 5 between the two. Itis ewise possible to confine the bank of latex between two rolls, oneplaced at I as at present and'one replacing the doctor I.

Various other modifications will occur to those skilled in the art andit is not intended to limit the invention other than as set forth in theappended claims.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A process for impregnating textile sheet material with an aqueousdispersion of rubber comprising advancing the material, applying the 4and confine the aqueous dispersion of rubber to one surface of thematerial and driving the dispersion univ formly into and through thematerial, so that it exudes upon the opposite surface thereof, anddistributing the dispersion which has been extruded through theinterstices of the material smoothly and uniformly over the oppositesurface of the material to form a continuous film thereover. A 2.-Aprocess for impregnating textile sheet "material with an aqueousdispersion of rubber comprising treating either or both of the sheetmaterial and the dispersion so that the sheet material is readily wettedby said dispersion, advancing the material, applying the aqueousdispersion of rubber to one surface of the material and driving thedispersion uniformly into and through the material to the oppositesurface thereof, and distributing the dispersion which has been extrudedthrough the interstices of the material smoothly and uniformly over theopposite surface of the material to form a continuous film thereover.

3. A process for impregnating fabric with an aqueous dispersion ofrubber, said fabric and dispersion being mutually wettable, which comprises applying the aqueous dispersion of rubber, driving the dispersionuniformly into and through the fabric to the opposite surface thereof,and distributing the dispersion which has been extruded through theinterstices of the fabric smoothly and uniformly over the oppositesurface of the material to form a continuous film thereover.

